The goal of this project is to characterize the defects in Natural Killer (NK) cell development in the context of aging through analysis of progenitor cells. Aim 1 proposes to characterize the developmental stage(s) in which NK development is abrogated in aged mice. Analyzing young and aged mice by means of 12 color combinatorial FACS analyses we will deduce the discrete step of NK differentiation that is affected by aging. Cell surface markers specific for NK developmental stages, from the earliest common lymphoid progenitor (CLP) to the NK committed progenitor (NKP) to fully mature NK cells, will be assessed to distinguish where NK development in affected. Also, mature NK subsets, defined by CD27 and Mac1 expression, from bone marrow, spleen, liver and lymph nodes will be assayed for their functional competence. The two hallmarks of NK effector function, cytolytic killing and cytokine secretion, will be compared between young and aged mice to characterize defects with respect to these pathways. Aim 2 will focus on verifying if the defects identified in aim 1 are cell intrinsic or extrinsic. Transplantations of NKP from young and aged mice into aged and young congenic host, respectively, will allow us to characterize the cell autonomous and/or microenvironment defects that are manifested with age. To find specific molecules that govern the cell intrinsic defects identified above, we will use Affymetrix microarrays to compare the differential gene expression between CLP and NKP from young and aged mice. This will allow us to identify specific transcription factors and signaling molecules that govern NK fate decisions. PUBLIC HEALTH RELEVANCE: NK cells play a pivotal role in fighting infection and tumor formation, both of which have a higher prevalence in the aged population. Thus, understanding of processes that lead to NK cell defects in aged individuals will be a critical first step for the development of therapies aimed at these age-dependent pathophysiological conditions.)